Hi S.,
I have a 4-year-old daughter and a 5 1/2 month old son. We have had our share of sleep problems, so I sympathize with you! I would probably chalk this up to plain old fussiness. I know both my kids were fussy (especially in the evening) from 6 weeks to around 3 months, and it seemed nothing would calm them. It started decreasing gradually from there, and they got on a more normal schedule eventually.
Also, my son only napped for an hour at a time (4 1-hour naps a day, usually, which made for a strange schedule) up until around 4-5 months. (My daughter totally resisted naps) Now my son's doing 2 longer naps a day. As long as you know he is not ill, I think both the fussiness and sleeping are developmental and will change with time, so hang in there!
I'd recommend reading up on sleep if you haven't already, and trying to start setting the patterns you want, whether it's family bed or baby-in-the-crib or whatever. Books you might try are The Baby Whisperer; Healthy Sleep Habits, Happy Child; and The No-Cry Sleep Solution. That would give you a range of approaches so you can see what's right for you. (You may have already read these...) Since we had a very rough sleep road with our first, we have been really trying with our son to set good sleep patterns, and so far it's going better.
Good luck! Having just been through the newborn/early infanthood stage, I really think that when they are that young, a lot of things happen that are hard for us to figure out and that it all works out eventually... :-)But it seems like once one thing is fixed, another issue arises. My son has recently decided that he wants to get up at 9:00 pm, about 3 hours after going to bed. :-(
K.